The present invention is directed, in general, to a semiconductor device and, more specifically, to a semiconductor device having a high-K gate dielectric and a method of manufacture thereof.
In order to produce the required drive currents for state-of-the-art submicron devices, high gate capacitance is essential. Because gate stack capacitance is directly proportional to the material dielectric constant (K) and inversely proportional to the dielectric material thickness, either of these factors may be varied appropriately to increase the overall gate stack capacitance. Silicon dioxide (SiO2) has long been the gate dielectric material of choice. Decreasing the gate dielectric thickness, which is typically a silicon dioxide (SiO2) layer, has reached its functional limit in devices with sizes in the lower submicron range. Because SiO2 has a relatively low dielectric constant (K=3.9), such scaling soon results in SiO2 layers so thin (from about 1.0 nm to about 1.5 nm) that excessive leakage current compromises transistor performance. Therefore, alternative higher-dielectric constant gate materials will be required as device sizes become ever smaller. It has been widely suspected that an underlayer, between the silicon substrate and the high-K dielectric layer, will be needed to facilitate growth of the high-K dielectric layer, as well as to enhance the electrical properties of the interface. However, both this underlayer and the high-K dielectric layer should be as thin as possible in order to minimize the effective oxide thickness (EOT) of the gate dielectric stack and maximize the capacitance. High capacitance enables the transistor to turn on and off more effectively.
However, other elements/compounds such as aluminum oxide (Al2O3), zirconium oxide (ZrO2), hafnium oxide (HfO2) and titanium oxide (TiO2) that have higher dielectric constants ranging from about 10 to about 80 are not xe2x80x9cnativexe2x80x9d to the silicon that typically forms the substrate. That is to say, they all require the introduction of some other material to form the dielectric other than the conventional method of exposing silicon to oxygen with heat thereby forming the SiO2 dielectric. Thus, higher-K dielectrics must be deposited in a separate step requiring additional controls and incurring additional problems of uneven growth, addition of an extraneous metallic element to silicon/silicon dioxide, etc. Thus, the silicon/silicon dioxide interface is highly desirable but for its limited application in extremely small submicron devices.
In order to facilitate growth of a high-K dielectric gate material during an atomic layer deposition (ALD) process, the surface upon which the high-K dielectric gate material is to be deposited should be substantially-hydroxylated. That is, high OH surface concentrations are more suitable to provide nucleation for ALD of the high-K gate material. However, the difficulty of forming a uniform, hydroxylated surface suitable for a subsequent ALD process is extremely problematic.
For example, two thermal processes, i.e., rapid thermal oxidation and rapid thermal oxynitridation, are commonly used to form such a surface. However, thermal oxide surfaces contain a low hydroxyl content. In addition, the growth rate and uniformity are difficult to control, resulting in an uneven underlayer.
Accordingly, what is needed in the art is a gate dielectric structure and method of forming the same that do not exhibit the limitations of the prior art.
To address the above-discussed deficiencies of the prior art, the present invention provides in one embodiment a method of manufacturing a semiconductor device comprising providing a semiconductor substrate, forming a substantially-hydroxylated SiOxHy layer on the semiconductor substrate in a presence of oxygen and hydrogen, and forming a metallic oxide, high-K dielectric layer on the substantially-hydroxylated SiOxHy layer. The substantially-hydroxylated SiOxHy layer has a surface concentration of hydroxyl (OH) species equal to or greater than about 3xc3x971014 hydroxyl per cm2.
The foregoing has outlined preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention.